1. Field of the Invention
The invention is directed in general toward an automotive power distribution box cover and more specifically to a flame retardant cap for mounting within the cover to fit over a high current connection.
2. Discussion of Related Art
An electrical junction block or power distribution box (PDB) is commonly used in automotive vehicles to streamline electrical system wiring by eliminating multi-branch wiring. The PDB consolidates fuses, branch circuits, relays, connectors and other electrical components in a single location. This is typically done by incorporating a bus bar or similar conductor into a housing. The housing often includes a surface having a plurality of receptacles for receiving the electrical connectors, fuses, relays and other circuit components. The bus bar is routed beneath the surface and has a plurality of blade-like projections that project into some or all of the receptacles to make electrical contact with the components. The bus bar is used to supply electrical power to the components for serving the vehicle electrical circuit requirements. The electrical power is usually provided to the bus bar through a power supply line from the vehicle alternator and/or battery.
As illustrated in U.S. Pat. No. 6,322,376, a high current connection between the vehicle battery and the PDB is often made by connecting power cables through a terminal to a plate section of the bus bar. A stud bolt mounted in a holder on the PDB extends through apertures in the terminal and bus bar plate section. A nut fastens the terminal onto the bus bar plate section. In this type of high current connection, if the terminal is improperly or inadequately connected to the bus bar, electrical arcing can ignite the PDB housing. In the above-identified patent, the stud bolt holder is made with flame-retardant material so it melts rather than ignites in the event of such a condition. Therefore, only the holder needs to be replaced, and the PDB housing is not damaged.
However, power distribution boxes are provided with plastic covers that are also in danger of igniting if the high current connection becomes loose. While wiring device covers are sometimes made of flame-retardant material, for example as disclosed in U.S. Pat. No. 4,541,538, covers for vehicle power distribution boxes have become rather large as the boxes have expanded in size to meet the increased electric circuit requirements of today's vehicles. Flame-retardant material is relatively expensive as compared to the traditional electrically non-conductive plastic material used for the covers. For production of large numbers of PDB covers, the augmented cost of making the entire covers from flame-retardant material becomes quite significant.